I would have to say I have not finished many series in entirety, but I am reading a ton that are ongoing.
I use Baka Updates to keep track of what I am reading - I have 214 series listed. 35 on my wish list.

Now that I think of it, haven't read very many series to the bitter end, especially considering how many series I'm familiar with. I guess because most of what I've read is either still being published, or was discontinued by the English licenser.

errrrrrrr i dont really keep count but if i had to gez about 200 might even be 300 and then alot of incomplete and reread some series about in total 50 times and im still reading alot of ones still ongoing

the sad thing is tho i know ive read alot and cuz of that i start to forget series names and cant find them when i wanna reread them